Cariboo
Forest
Region
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Sheep Grazing for Vegetation Control
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Extension Note EN16
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Animals have been used to graze vegetation in forests throughout the
world. Livestock are often used in agroforestry, in which agricultural
crops are grown under a forest canopy, to help control unwanted vegetation
while gaining extra forage.
The use of sheep has been less extensive in British Columbia and began
in the Cariboo Forest Region in 1984. That summer, sheep grazed a cutblock
dominated by fireweed near Hendrix Lake (ICHmk3) in the 100 Mile House
Forest District to extend their area of summer range. The block had been
planted with spruce, and observations of the grazing showed relatively
little damage to the seedlings. Trials of this method of vegetation control
have since been implemented in the Horsefly and Quesnel Districts in the
Cariboo, and sheep grazing has become a considerable source of research
work and media attention. In 1993, sheep grazed 450 hectares on two projects
to control competing vegetation on cutblocks in the Cariboo Forest Region.
Objectives
The objectives of the Cariboo Region's sheep grazing program are:
-
to improve the survival and growth of seedlings by controlling competing
vegetation
-
to test sheep grazing as a site preparation and brushing vegetation management
tool
Why Sheep?
Sheep grazing has been shown to be an effective method for controlling
vegetation. It can provide an alternative to chemical brush control, and
in some cases can be used where herbicides cannot be applied. Grazing sheep
on cutblocks is a good example of integrated resource management and has
high public acceptance as a forest management practice.
Target Vegetation
Research to date shows that sheep graze selectively. They readily graze
fireweed and grasses, but prefer a combination of species. Monitoring of
grazing at Moffat Creek (ESSFwk1) in 1993 showed a high preference for
fireweed and horsetails with little thimbleberry removed. At Boss Creek
(ESSFwk1), cow parsnip and false Solomon's seal were grazed along with
fireweed, but again, little thimbleberry was removed. Raspberry is also
not grazed readily by sheep. Willow and alder shrubs are grazed as high
as the sheep can reach, and sheep will sometimes trample willow stems to
graze on the branch ends. The following list summarizes sheep preference
for some common species of target vegetation.
| Preferred Species |
Less Preferred Species |
Fireweed
Grasses
Sitka Valerian
Aspen
Willow |
Thimbleberry
Rasberry
Huckleberry
Paper birch
Alder
Twinberry
Bracken fern
Indian hellebore |
Some findings on sheep grazing preferences are:
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Sheep prefer new, succulent growth, whether it is the spring flush or regrowth
after a first graze.
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Vegetation degraded by frost or drought has reduced palatability.
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Target vegetation should be less than 1m tall so that the sheep can graze
the entire plant.
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Target vegetation must not be woody, as sheep will leave fireweed stems
and graze only the leaves in the late summer
Sheep also have a varying preference for conifers. Current data show that
the least preferred species is spruce, followed by Douglas-fir. Pine is
the most preferred. Although some pine plantations have been successfully
grazed, others have not. Grazing sheep on a pine plantation requires intensive
sheep management and is currently not recommended.
Seedlings are most susceptible to damage immediately after planting
and when flushing. Sheep may browse the succulent new foliage and cause
mechanical damage to new leaders while moving through the block.
Sheep Management
Proper management of the sheep flock is critical to achieve even vegetation
removal over the entire cutblock. Some recommended sheep management techniques
are:
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Keep the sheep together as a cohesive unit.
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Avoid trampling damage to seedlings by moving the sheep only once over
any given portion of the block and using roads and skid trails to move
sheep to and from the grazing area.
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Hire experienced shepherds.
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Use well-trained dogs.
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Camp next to night corrals to ward off predators.
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Never leave the sheep unattended
Site Characteristics
Some of the site characteristics required for sheep grazing are:
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Less than 50% slope
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Sufficient water for the sheep without the potential for contamination
of watercourses
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Low slash that will not block or injure the sheep
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Few gullies or features that hide sheep or predators
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Accessibility to a main road for transporting the sheep
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Proximity to alternative blocks for grazing in the event of unacceptable
seedling damage, and
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Proximity to other cutblocks planned for grazing to reduce mid-season transportation
Other Resource Concerns
The effects of sheep grazing projects on wildlife and environmental factors
must be considered at all stages of grazing projects. Standards under the
Forest Practices Code will bring restrictions and new requirements for
grazing sheep on cutblocks.
Disease transmission from domestic sheep must not affect wild sheep
populations. Predation on sheep by carnivores must be minimized to avoid
any destruction of wildlife. Furthermore, water quality on sites grazed
by sheep cannot be compromised, and soil compaction from sheep activity
should be minimal.
Vegetation Removal
Grazing is most effective on new sprouts found either in the spring or
on regrowth following grazing. Grazing should leave 5 to 15% of the target
vegetation cover so that the sheep do not begin damaging seedlings when
their forage supply becomes low. A minimum of two to three passes will
be required to weaken the target vegetation and release conifer seedlings
from competition. Grazing on regrowth in the same year is considered a
second pass.
Research Results
Seven-year results at the Doreen Creek trial show significant control of
fireweed by grazing and by Vision herbicide compared to the untreated control.
The trial also shows a slight, but insignificant, seedling growth increase
on the areas grazed and those treated with Vision herbicide compared to
the control. However, vegetation competion was only moderate on this site.
Other sites have not shown seedling growth increases from grazing because
of seedling damage, poor initial seedling vigour, or insufficient time
since trial establishment to form conclusions.
Publications
Newsome, T., B. Wikeem and C. Sutherland. 1994. Sheep Grazing Guidelines
for Managing Vegetation on Forest Plantations in British Columbia.
Land Mgmt. Hdbk. #34.
Contact
For more information on the sheep grazing research monitoring program,
please contact Teresa Newsome,
Research Silviculturist, at 250-398-4408.
* This Extension Note was based on a presentation given
by Teresa Newsome to the Integrated Forest Vegetation Management Conference
in Richmond, November 1993.
| Summary Of Current Knowledge |
| Sheep will control some species of vegetation, such as fireweed and
grass. |
| New sprouts are more palatable and nutritious to sheep. |
| Potential seedling damage varies by species. Spruce is the least susceptible
to damage, followed by Douglas-fir and pine. |
| Grazing with two to three passes can achieve comparable vegetation
control results to Vision herbicide, but at a considerably higher cost. |
| Proper management of sheep on the block is essential to successful
vegetation management by grazing. |
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